Methods of forming transistors with retrograde wells in CMOS applications and the resulting device structures

ABSTRACT

A method includes forming a layer of silicon-carbon on an N-active region, performing a common deposition process to form a layer of a first semiconductor material on the layer of silicon-carbon and on the P-active region, masking the N-active region, forming a layer of a second semiconductor material on the first semiconductor material in the P-active region and forming N-type and P-type transistors. A device includes a layer of silicon-carbon positioned on an N-active region, a first layer of a first semiconductor positioned on the layer of silicon-carbon, a second layer of the first semiconductor material positioned on a P-active region, a layer of a second semiconductor material positioned on the second layer of the first semiconductor material, and N-type and P-type transistors.

BACKGROUND OF THE INVENTION

1. Field of the Invention

Generally, the present disclosure relates to the manufacture ofsophisticated semiconductor devices, and, more specifically, to variousmethods of forming transistor devices with retrograde wells in CMOS(Complementary Metal Oxide Semiconductor) applications, and theresulting device structures.

2. Description of the Related Art

The fabrication of advanced integrated circuits, such as CPU's, storagedevices, ASIC's (application specific integrated circuits) and the like,requires the formation of a large number of circuit elements in a givenchip area according to a specified circuit layout, wherein so-calledmetal oxide field effect transistors (MOSFETs or FETs) represent oneimportant type of circuit element that substantially determinesperformance of the integrated circuits. A FET is a device that typicallyincludes a source region, a drain region, a channel region that ispositioned between the source region and the drain region, and a gateelectrode positioned above the channel region. Current flow through theFET is controlled by controlling the voltage applied to the gateelectrode. If a voltage that is less than the threshold voltage of thedevice is applied to the gate electrode, then there is no current flowthrough the device (ignoring undesirable leakage currents, which arerelatively small). However, when a voltage that is equal to or greaterthan the threshold voltage of the device is applied to the gateelectrode, the channel region becomes conductive, and electrical currentis permitted to flow between the source region and the drain regionthrough the conductive channel region. The above description isapplicable for both the N-type FET as well as the P-type FET, exceptthat the polarity of voltage in operation and the doping type of thesource, the channel and the drain regions are correspondingly reversed.In so-called CMOS (Complementary Metal Oxide Semiconductor) technology,both N-type and P-type MOSFETs (which are referred to as being“complementary” to each other) are used in integrated circuit products.CMOS technology is the dominant technology as it relates to themanufacture of almost all current-day large scale logic and memorycircuits.

To improve the operating speed of FETs, and to increase the density ofFETs on an integrated circuit device, device designers have greatlyreduced the physical size of FETs over the years. More specifically, thechannel length of FETs has been significantly decreased, which hasresulted in improving the switching speed of FETs. However, decreasingthe channel length of a FET also decreases the distance between thesource region and the drain region. In some cases, this decrease in theseparation between the source and the drain makes it difficult toefficiently inhibit the electrical potential of the channel from beingadversely affected by the electrical potential of the drain, which iscommonly referred to as a “punch-through” of the electrical potentialfrom the drain to the source and leads to larger leakage currents. Thisis sometimes referred to as a so-called short channel effect, whereinthe characteristic of the FET as an active switch is degraded.

In contrast to a planar FET, which has a planar structure, there areso-called three-dimensional (3D) devices, such as an illustrative FinFETdevice, which is a three-dimensional structure. More specifically, in aFinFET, a generally vertically positioned, fin-shaped active area isformed and a gate electrode encloses both of the sides and the uppersurface of the fin-shaped active area to form a “tri-gate” structure soas to use a channel having a 3D “fin” structure instead of a planarstructure. In some cases, an insulating cap layer, e.g., siliconnitride, is positioned at the top of the fin and the FinFET device onlyhas a dual-gate structure. Unlike a planar FET, in a FinFET device, achannel is formed perpendicular to a surface of the semiconductingsubstrate so as to reduce the depletion width in the “fin” channel (as aresult of the better electrostatic characteristics of the tri-gate ordual-gate structure around the fin channel) and thereby reduce so-calledshort channel effects. Also, in a FinFET, the junction capacitance atthe drain region of the device is greatly reduced, which tends to reduceat least some short channel effects.

In one embodiment, FinFET devices have been formed on so-calledsilicon-on-insulator (SOI) substrates. An SOI substrate includes a bulksilicon layer, an active layer and a buried insulation layer made ofsilicon dioxide (a so-called “BOX” layer) positioned between the bulksilicon layer and the active layer. Semiconductor devices are formed inand above the active layer of an SOI substrate. The fins are formed inthe active layer and the buried insulation layer provides good isolationbetween adjacent fins. The processes used to form FinFET devices on SOIsubstrates have relatively good compatibility with various processesthat are performed when forming planar transistor devices in CMOSapplications. For example, in both applications, the gate stack and thegate insulation layer can be made of the same materials (as in planarCMOS on SOI), e.g., poly-SiON or high-k/metal-gate (HKMG), and bothapplications may involve performing various epitaxial silicon growthprocesses (e.g., SiGe for PMOS and raised SD for NMOS) as well as theformation of epi-silicon material on the fins so as to define thesource/drain regions from the FinFET devices that provide goodresistance and desirable stress characteristics. When an appropriatevoltage is applied to the gate electrode of a FinFET device, thesurfaces (and the inner portion near the surface) of the fins, i.e., thesubstantially vertically oriented sidewalls and the top upper surface ofthe fin with inversion carriers, contributes to current conduction. In aFinFET device, the “channel-width” is approximately two times (2×) thevertical fin-height plus the width of the top surface of the fin, i.e.,the fin width. Multiple fins can be formed in the same foot-print asthat of a planar transistor device. Accordingly, for a given plot space(or foot-print), FinFETs tend to be able to generate significantlystronger drive current than planar transistor devices. Additionally, theleakage current of FinFET devices after the device is turned “OFF” issignificantly reduced as compared to the leakage current of planartransistor MOSFETs due to the superior gate electrostatic control of the“fin” channel on FinFET devices. In short, the 3D structure of a FinFETdevice is a superior MOSFET structure as compared to that of a planarMOSFET, especially in the 20 nm CMOS technology node and beyond.

The formation of transistor devices in CMOS technology has also evolvedand continues to evolve to produce devices with improved operationalcharacteristics. One relatively recent advance involves the use of lowchannel doping (i.e., super-steep channel doping profiles) for deeplydepleted channel regions during device operation, where there aremultiple epi layers (i.e., Boron-doped-Silicon (Si:B), Carbon-dopedSilicon (Si:C) and non-doped Silicon) formed above N/P wells. In such adevice, the suppression of boron (B), phosphorous (P) and arsenic (As)diffusion is mainly due to the presence of the carbon-doped siliconlayer (Si:C) layer. Alternatively, instead of using epitaxial growthprocesses, the B-doped and C-doped silicon layers can be formed byimplanting boron and carbon into the silicon substrate in both the N andP active regions of the substrate. The low doping of the channel regionmay suppress or reduce the so-called “short-channel effect” typicallyfound on traditional planar transistor devices manufactured on bulksilicon, reduce variations in the threshold voltages of such devices(due to less random dopant fluctuations), reduce source/drain leakagecurrents (by punch-through suppression by those doped layers below thechannel) and lower junction capacitances. Therefore, MOSFET devicesformed on a bulk substrate with a low doped channel can enjoy theadvantages of devices with fully depleted channel regions duringoperations as if they are fabricated on an SOI substrate.

It is generally known that fully depleted devices with a substantiallyun-doped or low-doped channel region are effective in reducing thresholdvoltage variability due to the elimination of random dopant fluctuationsin such devices, and that such devices exhibit improved deviceperformance with relatively low dynamic power requirements, low leakagecurrents and relatively high transistor density. The fully depleteddevices can take the form of planar transistor devices with ultra-thinbodies formed on SOI substrates or three-dimensional devices, such asFINFET devices. However, the planar devices consume a substantial amountof plot space (or foot-print) in the channel width direction and, withrespect to FINFET technology, there are significant challenges informing deep fin/isolation trenches and filling such trenches withoutcreating undesirable voids.

The present disclosure is directed to various methods of formingtransistor devices with retrograde wells in CMOS applications, and theresulting device structures, that may solve or reduce one or more of theproblems identified above.

SUMMARY OF THE INVENTION

The following presents a simplified summary of the invention in order toprovide a basic understanding of some aspects of the invention. Thissummary is not an exhaustive overview of the invention. It is notintended to identify key or critical elements of the invention or todelineate the scope of the invention. Its sole purpose is to presentsome concepts in a simplified form as a prelude to the more detaileddescription that is discussed later.

Generally, the present disclosure is directed to various methods offorming transistor devices with retrograde wells in CMOS applications,and the resulting device structures. One illustrative method disclosedherein includes forming an N-active region and a P-active region in asemiconductor substrate, forming a first masking layer that covers theP-active region while leaving an area above the N-active regionun-masked, forming a layer of silicon-carbon on an upper surface of theN-active region, performing a common deposition process to form a firstportion of a layer of a first semiconductor material on the layer ofsilicon-carbon and a second portion of the first semiconductor materialon an upper surface of the P-active region, masking the N-active regionwhile leaving an area above the P-active region un-masked, forming alayer of a second semiconductor material on the second portion of thefirst semiconductor material, forming an N-type transistor in and abovethe N-active region and forming a P-type transistor in and above theP-active region.

Another illustrative method disclosed herein involves forming anN-active region and a P-active region in a semiconductor substrate,masking the P-active region, forming a layer of silicon-carbon on anupper surface of the N-active region and forming a first layer of afirst semiconductor material on the layer of silicon-carbon, masking theN-active region, forming a second layer of the first semiconductormaterial on an upper surface of the P-active region and forming a layerof a second semiconductor material on the second layer of the firstsemiconductor material, forming an N-type transistor in and above theN-active region and forming a P-type transistor in and above theP-active region.

Yet another illustrative method disclosed herein involves forming anN-active region and a P-active region in a semiconductor substrate,masking the N-active region, forming a first layer of a firstsemiconductor material on an upper surface of the P-active region andforming a layer of a second semiconductor material on the first layer ofthe first semiconductor material, masking the P-active region, forming alayer of silicon-carbon on an upper surface of the N-active region andforming a second layer of the first semiconductor material on the layerof silicon-carbon, forming an N-type transistor in and above theN-active region and forming a P-type transistor in and above theP-active region.

One illustrative device disclosed herein includes a substrate comprisedof an N-active region and a P-active region, a layer of silicon-carbonpositioned on an upper surface of the N-active region, a first layer ofa first semiconductor positioned on the layer of silicon-carbon, asecond layer of the first semiconductor material positioned on an uppersurface of the P-active region, a layer of a second semiconductormaterial positioned on the second layer of the first semiconductormaterial, an N-type transistor positioned above the N-active region anda P-type transistor positioned above the P-active region.

BRIEF DESCRIPTION OF THE DRAWINGS

The disclosure may be understood by reference to the followingdescription taken in conjunction with the accompanying drawings, inwhich like reference numerals identify like elements, and in which:

FIGS. 1A-1G depict one illustrative embodiment disclosed herein forforming transistor devices with retrograde wells in CMOS applications;

FIGS. 2A-2E depict another illustrative method disclosed herein offorming transistor devices with retrograde wells in CMOS applications;and

FIGS. 3A-3E depict yet another illustrative method disclosed herein offorming transistor devices with retrograde wells in CMOS applications.

While the subject matter disclosed herein is susceptible to variousmodifications and alternative forms, specific embodiments thereof havebeen shown by way of example in the drawings and are herein described indetail. It should be understood, however, that the description herein ofspecific embodiments is not intended to limit the invention to theparticular forms disclosed, but on the contrary, the intention is tocover all modifications, equivalents, and alternatives falling withinthe spirit and scope of the invention as defined by the appended claims.

DETAILED DESCRIPTION

Various illustrative embodiments of the invention are described below.In the interest of clarity, not all features of an actual implementationare described in this specification. It will of course be appreciatedthat in the development of any such actual embodiment, numerousimplementation-specific decisions must be made to achieve thedevelopers' specific goals, such as compliance with system-related andbusiness-related constraints, which will vary from one implementation toanother. Moreover, it will be appreciated that such a development effortmight be complex and time-consuming, but would nevertheless be a routineundertaking for those of ordinary skill in the art having the benefit ofthis disclosure.

The present subject matter will now be described with reference to theattached figures. Various structures, systems and devices areschematically depicted in the drawings for purposes of explanation onlyand so as to not obscure the present disclosure with details that arewell known to those skilled in the art. Nevertheless, the attacheddrawings are included to describe and explain illustrative examples ofthe present disclosure. The words and phrases used herein should beunderstood and interpreted to have a meaning consistent with theunderstanding of those words and phrases by those skilled in therelevant art. No special definition of a term or phrase, i.e., adefinition that is different from the ordinary and customary meaning asunderstood by those skilled in the art, is intended to be implied byconsistent usage of the term or phrase herein. To the extent that a termor phrase is intended to have a special meaning, i.e., a meaning otherthan that understood by skilled artisans, such a special definition willbe expressly set forth in the specification in a definitional mannerthat directly and unequivocally provides the special definition for theterm or phrase.

The present disclosure is directed to various methods of formingtransistor devices with retrograde wells in CMOS applications, and theresulting device structures. As will be readily apparent to thoseskilled in the art upon a complete reading of the present application,the novel methods and devices disclosed herein may be employed inmanufacturing a variety of different devices, including, but not limitedto, logic devices, memory devices, ASICs, etc. With reference to theattached figures, various illustrative embodiments of the methods anddevices disclosed herein will now be described in more detail.

FIGS. 1A-1G show a simplified view of one illustrative embodiment of anintegrated circuit product or device 10 disclosed herein at an earlystage of manufacturing. The device 10 is formed above an illustrativesubstrate 12. The substrate 12 may have a variety of configurations,such as the depicted bulk substrate configuration. The substrate 12 mayalso have an SOI (silicon-on-insulator) configuration wherein thesemiconductor devices are formed in the active layer of the SOIsubstrate. The substrate 12 may be made of silicon or it may be made ofmaterials other than silicon. Thus, the terms “substrate,”“semiconductor substrate” or “semiconducting substrate” should beunderstood to cover all semiconducting materials and all forms of suchmaterials. The inventions disclosed herein will be disclosed in thecontext of forming planar transistor devices for the integrated circuitproduct 10. However, as will be recognized by those skilled in the artafter a complete reading of the present application, the inventionsdisclosed herein may be applied to the formation of planar FET devicesas well as 3D devices, such as FinFET devices.

With continuing reference to FIG. 1A, a plurality of trench isolationstructures 14 are formed in the substrate 12 using known masking,deposition and etching techniques. The trench isolation structures 14separate the substrate 12 into a P-active region 12P, where a P-typetransistor will be formed, and an N-active region 12N, where an N-typetransistor will be formed. After the isolation regions 14 are formed,various doped regions are formed in the active regions 12P, 12N byperforming known ion implantation processes and using appropriatemasking layers. For example, various ion implantation processes wouldhave been performed to form a so-called P-well (not shown) in theP-active region 12P and a so-called N-well (not shown) in the N-activeregion 12N. Thereafter, with continuing reference to FIG. 1A, a commonetching process, such as a reactive ion etching (RIE) process or a wetetching process, may be performed on the substrate 12 to define recesses15 in both the P-active region 12P and the N-active region 12N. Thedepth 15D of the recesses may vary depending upon the particularapplication, e.g., about 5-20 nm. The depth of the recesses 15 istypically optimized so as to avoid or minimize a step height differencebetween the completed active regions and the STI regions 14. After therecesses 15 are formed, so-called threshold voltage adjustingimplantation processes may have been performed on both of the activeregions 12P, 12N, using the appropriate masking layers during suchimplantation processes. One or more anneal processes may then beperformed to drive-in the various implanted materials. Note, however,using the methods disclosed herein, the substrate 12 is not subjected tothe typical carbon ion implantation process that is performed to formdoped carbon regions that act as a diffusion barrier layer to preventthe diffusion of the implanted materials that define the P-well andN-well back into the channel regions of the transistor devices that willbe formed above the active regions 12P, 12N. Also depicted in FIG. 1A isan illustrative insulating layer 16, e.g., a pad oxide layer, that hasbeen formed on the active regions 12P, 12N by performing a thermaloxidation process.

FIG. 1B depicts the device 10 after a patterned hard mask layer 18 hasbeen formed above the P-active region 12P. The patterned hard mask layer18 leaves the area above the N-active region 12N exposed or un-maskedfor further processing. The patterned hard mask layer 18 may becomprised of a variety of materials, e.g., silicon nitride, and itsthickness may vary depending upon the particular application, e.g.,30-40 nm. The patterned mask layer 18 may be formed byblanket-depositing a layer of the hard mask material across thesubstrate 12, forming a patterned photoresist mask layer (not shown)above the layer of hard mask material and thereafter performing anetching process through the patterned photoresist mask layer to therebyremove the exposed portions of the deposited layer of hard maskmaterial. The patterned photoresist mask may be formed using knownphotolithography tools and techniques. The initial layer of hard maskmaterial may be deposited using a variety of known deposition processes,e.g., a chemical vapor deposition (CVD) process. FIG. 1B depicts thedevice 10 after the patterned layer of photoresist (that was used informing the patterned hard mask layer 18) has been removed.

FIG. 1C depicts the product 10 after several process operations havebeen performed. First, with the patterned hard mask layer 18 inposition, an etching/cleaning process was performed to remove the layerof insulating material 16 from above the N-active region 12N. Thisetching/cleaning process may be a traditional epi-preclean process thatis performed prior to performing an epitaxial growth process on theexposed surface of the active region 12N. In one example, a chemicalsuch as SiCoNi may be used as part of this cleaning process. Second,after the epi pre-clean process is performed such that the upper,recessed surface of the active region 12N is exposed and free ofundesirable contaminants, a semiconductor material layer 20 was formedon the exposed surface of the N-active region 12N by performing anepitaxial deposition process. In one illustrative embodiment, thesemiconductor material layer 20 is comprised of silicon-carbon (e.g.,about 1-2% carbon) having a thickness of about 5-10 nm. In theillustrative case where the semiconductor material layer 20 is comprisedof silicon-carbon, it may be formed in an epi-reactor using a mixture ofSiH₂Cl₂ and SiH₃CH₃ as precursor materials supplied to the reactor atflow rates that fall within the range of about 3-10 sccm for SiH₃CH₃ andabout 50-200 sccm for SiH₂Cl₂. The epitaxial deposition process may beperformed at a temperature that falls within the range of about 600-800°C. at a pressure that falls within the range of about 10-20 Torr.

FIG. 1D depicts the product 10 after several additional processoperations have been performed. First, the patterned hard mask layer 18was removed. Second, another etching/cleaning process was performed toremove the layer of insulating material 16 from above the P-activeregion 12P and to clean the upper surface of the semiconductor materiallayer 20. This etching/cleaning process may be a traditional epipre-clean process that is performed prior to performing an epitaxialgrowth process. Third, after the epi pre-clean process was performed, asemiconductor material layer 22 was formed above both of the activeregions 12P, 12N. More specifically, a first portion 22P of thesemiconductor material layer 22 was formed on the exposed, recessedsurface of the P-active region 12P, while a second portion 22N of thesemiconductor material layer 22 was formed on the semiconductor materiallayer 20. Note that both of the portions of the semiconductor materiallayer 22 depicted in FIG. 1D were formed in a single, common depositionprocess. In one illustrative embodiment, the semiconductor materiallayer 22 is comprised of silicon, and it has a thickness of about 5-15nm. In the illustrative case where the semiconductor material layer 22is comprised of silicon, it may be formed in an epi-reactor usingSiH₂Cl₂ precursor materials supplied to the reactor at flow rates thatfall within the range of about 150-250 sccm. The epitaxial depositionprocess may be performed at a temperature that falls within the range ofabout 700-800° C. at a pressure that falls within the range of about10-20 Torr.

FIG. 1E depicts the device 10 after several additional processoperations have been performed. First, a patterned hard mask layer 24was formed above the N-active region 12N. The patterned hard mask layer24 leaves the area above the P-active region 12P, and particularly thesemiconductor material layer 22P, exposed or un-masked for furtherprocessing. The patterned hard mask layer 24 may be comprised of thesame materials and formed using the same techniques as those describedabove for the patterned hard mask layer 18. Second, with the patternedhard mask layer 24 in position, an etching/cleaning process is performedto remove undesirable contaminants from the surface of the semiconductormaterial layer 22P. This may be accomplished by performing a traditionalepi pre-clean process that is performed prior to performing an epitaxialgrowth process on the exposed surface of the semiconductor materiallayer 22P. Second, after the upper surface of the semiconductor materiallayer 22P is cleared of undesirable contaminants, a semiconductormaterial layer 26 is formed on the exposed surface of the semiconductormaterial layer 22P by performing an epitaxial deposition process. Thesemiconductor material layer 26 may be comprised of a variety ofdifferent semiconductor materials, e.g., silicon-germanium, a III-Vmaterial, etc., and it may have a thickness of about 10-15 nm. In oneillustrative embodiment, the semiconductor material layer 26 iscomprised of silicon-germanium having a thickness of about 10-15 nm. Inthe illustrative case where the semiconductor material layer 26 iscomprised of silicon-germanium, it may be formed in an epi-reactor usingSiH₄/GeH₄ precursor materials supplied to the reactor at flow rates thatfall within the range of about 50-200 sccm for SiH₄ with about 10-50%being GeH₄. The epitaxial deposition process may be performed at atemperature that falls within the range of about 550-650° C. at apressure that falls within the range of about 2-20 Torr.

FIG. 1F depicts the device 10 after the patterned hard mask layer 24 hasbeen removed. At this point, various semiconductor devices, e.g.,transistors, may be formed in and above the active regions 12P, 12N.Note that, in the depicted example, the common deposition processdescribed in connection with FIG. 1D above was performed in such amanner that the upper surface 22ND of the second portion 22N of thesemiconductor material layer 22 is substantially level with an uppersurface of the isolation region 14. Additionally, in the depictedexample, the deposition process described in connection with FIG. 1Eabove was performed in such a manner that an upper surface 26U of thesemiconductor material layer 26 is substantially level with an uppersurface of the isolation region 14. Of course, the isolation region 14for the active regions 12P, 12N, need not be the same region, i.e., theactive regions 12P, 12N may be defined by totally separate isolationregions formed at spaced-apart locations in the substrate 12.

FIG. 1G depicts the device 10 after an illustrative and schematicallydepicted P-type transistor 30P and an illustrative and schematicallydepicted N-type transistor 30N have been formed in and above the activeregions 12P, 12N, respectively. In the embodiment depicted in FIG. 1G,the transistors 30P, 30N are depicted as being planar transistordevices. However, as noted previously, the inventions disclosed hereinmay be applied to the formation of planar FET devices and/or 3D devices,such as FinFET devices, for a particular integrated circuit product 10.In the depicted example, each of the transistors 30P, 30N is comprisedof a schematically depicted gate structure 32, a gate cap layer 34 and asidewall spacer structure 36. The gate structures 32 are comprised of anillustrative gate insulation layer 32A and an illustrative gateelectrode 32B. As will be recognized by those skilled in the art after acomplete reading of the present application, the gate structures 32 ofthe device 10 depicted in the drawings, i.e., the gate insulation layer32A and the gate electrode 32B, are intended to be representative innature. For example, the gate insulation layer 32A may be comprised of avariety of different materials, such as, for example, silicon dioxide, ahigh-k (k greater than 10) dielectric material (where k is thedielectric constant), etc. The gate electrode 32B may be comprised orone or more layers of conductive material, e.g., doped polysilicon, oneor more layers of metal, a metal nitride, etc. The gate structures 32may be formed using either “gate-first” or “replacement gate” (alsoknown as “gate-last”) techniques. Moreover, the materials used for thegate structure 32 on the P-type transistor 30P may be different from thematerials used for the gate structure 32 on the N-type transistor 30N.Although not depicted in FIG. 1G, at this point in the process flow,source/drain regions (not shown), e.g., raised or planar, would havebeen formed for the transistors 32P, 32N using traditional manufacturingtechniques. At the point of fabrication depicted in FIG. 1G, traditionalmanufacturing techniques may be employed to complete the fabrication ofthe integrated circuit product 10, e.g., the formation of variouscontact structures, the formation of various metallization layers, etc.

FIGS. 2A-2E depict another illustrative method disclosed herein offorming transistor devices with retrograde wells in CMOS applications.FIG. 2A depicts the device at a point of fabrication that corresponds tothat depicted in FIG. 1B, i.e., the patterned hard mask layer 18 hasbeen formed above the P-active region 12P. The patterned hard mask layer18 leaves the N-active region 12N exposed for further processing. FIG.2A depicts the device 10 after the patterned layer of photoresist (thatwas used in forming the patterned hard mask layer 18) has been removed.

FIG. 2B depicts the product 10 after several process operations havebeen performed. First, with the patterned hard mask layer 18 inposition, an etching/cleaning process was performed to remove the layerof insulating material 16 from above the N-active region 12N. Second,after the epi pre-clean process was performed, the above-describedsemiconductor material layer 20 was formed on the exposed recessedsurface of the N-active region 12N by performing an epitaxial depositionprocess. Then, with the patterned mask layer 18 still in position,another etching/cleaning process was performed to clean the uppersurface of the semiconductor material layer 20. After the epi pre-cleanprocess was performed, a semiconductor material layer 42 was then formedon the semiconductor material layer 20. In this embodiment, thesemiconductor material layer 42 may be made of the same materials asthose described above for the semiconductor material layer 22. In oneembodiment, the semiconductor material layer 42 may be formed such thatthe upper surface 42U of the semiconductor material layer 42 may besubstantially level with the upper surface of the isolation region 14.

FIG. 2C depicts the device 10 after several additional processoperations have been performed. First, the patterned hard mask layer 18was removed. Thereafter, another patterned hard mask layer 44 was formedabove the N-active region 12N. The patterned hard mask layer 44 leavesthe P-active region 12P exposed or un-masked for further processing. Thepatterned hard mask layer 44 may be comprised of the same materials andformed using the same techniques as those described above for thepatterned hard mask layer 18.

FIG. 2D depicts the device 10 after several other process operationswere performed. First, with the patterned hard mask layer 44 inposition, an etching/cleaning process was performed to remove the layerof insulating material 16 from above the P-active region 12P. In oneembodiment, the removal of the layer of insulating material 16 may bepart of a traditional epi pre-clean process that is typically performedprior to performing an epitaxial growth process. After the upper surfaceof the P-active region 12P was cleared of undesirable contaminants, asemiconductor material layer 46 was formed on the exposed surface of theP-active region 12P. In this embodiment, the semiconductor materiallayer 46 may be made of the same materials as those described above forthe semiconductor material layer 22. Then, with the patterned mask layer44 still in position, another etching/cleaning process was performed toclean the upper surface of the semiconductor material layer 46. Afterthe cleaning process was performed, the above-described semiconductormaterial layer 26 was then formed on the semiconductor material layer46. In one embodiment, the semiconductor material layer 26 may be formedsuch that the upper surface 26U of the semiconductor material layer 26may be substantially level with the upper surface of the isolationregion 14.

FIG. 2E depicts the device 10 after the patterned hard mask layer 44 hasbeen removed. At this point, various semiconductor devices, such as theillustrative transistors 30P, 30N shown in FIG. 1G, may be formed in andabove the active regions 12P, 12N, respectively.

FIGS. 3A-3E depict yet another illustrative method disclosed herein offorming transistor devices with retrograde wells in CMOS applications.Relative to the embodiment shown in FIGS. 2A-2E, in this embodiment, thevarious semiconductor materials are first formed above the P-activeregion 12P, followed by the formation of various semiconductor materialsabove the N-active region 12N.

FIG. 3A depicts the device at a point of fabrication that corresponds tothat depicted in FIG. 1B with the notable exception that the patternedhard mask layer 18 has been formed above the N-active region 12N. Inthis example, the patterned hard mask layer 18 leaves the P-activeregion 12P exposed for further processing. FIG. 3A depicts the device 10after the patterned layer of photoresist (that was used in forming thepatterned hard mask layer 18) has been removed.

FIG. 3B depicts the product 10 after several process operations havebeen performed. First, with the patterned hard mask layer 18 inposition, an etching/cleaning process was performed to remove the layerof insulating material 16 from above the P-active region 12P. Second,after the epi pre-clean process was performed, the above-describedsemiconductor material layer 46 was formed on the exposed surface of theP-active region 12P by performing an epitaxial deposition process. Then,with the patterned mask layer 18 still in position, anotheretching/cleaning process was performed to clean the upper surface of thesemiconductor material layer 46. After the cleaning process wasperformed, the above-described semiconductor material layer 26 was thenformed on the semiconductor material layer 46.

FIG. 3C depicts the device 10 after several other process operationshave been performed. First, the patterned hard mask layer 18 wasremoved. Thereafter, another patterned hard mask layer 48 was formedabove the P-active region 12P. The patterned hard mask layer 48 leavesthe N-active region 12N exposed or un-masked for further processing. Thepatterned hard mask layer 48 may be comprised of the same materials andformed using the same techniques as those described above for thepatterned hard mask layer 18.

FIG. 3D depicts the device 10 after several additional processoperations were performed. First, with the patterned hard mask layer 48in position, an etching/cleaning process was performed to remove thelayer of insulating material 16 from above the N-active region 12N.After the upper surface of the N-active region 12N was cleared ofundesirable contaminants, the above-described semiconductor materiallayer 20 was formed on the exposed surface of the N-active region 12N.Then, with the patterned mask layer 48 still in position, anotheretching/cleaning process was performed to clean the upper surface of thesemiconductor material layer 20. After the cleaning process wasperformed, the above-described semiconductor material layer 42 was thenformed on the semiconductor material layer 20.

FIG. 3E depicts the device 10 after the patterned hard mask layer 48 hasbeen removed. At this point, various semiconductor devices, such as theillustrative transistors 30P, 30N shown in FIG. 1G, may be formed in andabove the active regions 12P, 12N, respectively.

The particular embodiments disclosed above are illustrative only, as theinvention may be modified and practiced in different but equivalentmanners apparent to those skilled in the art having the benefit of theteachings herein. For example, the process steps set forth above may beperformed in a different order. Furthermore, no limitations are intendedto the details of construction or design herein shown, other than asdescribed in the claims below. It is therefore evident that theparticular embodiments disclosed above may be altered or modified andall such variations are considered within the scope and spirit of theinvention. Accordingly, the protection sought herein is as set forth inthe claims below.

What is claimed:
 1. A method, comprising: forming an N-active region and a P-active region in a semiconductor substrate; forming a first masking layer that covers said P-active region while leaving an area above said N-active region un-masked; with said first masking layer in position, forming a layer of silicon-carbon on an upper surface of said N-active region; removing said first masking layer; performing a common deposition process to form a first portion of a layer of a first semiconductor material on said layer of silicon-carbon and a second portion of said first semiconductor material on an upper surface of said P-active region; forming a second masking layer that covers said N-active region while leaving an area above said P-active region un-masked; with said second masking layer in position, forming a layer of a second semiconductor material on said second portion of said first semiconductor material; removing said second masking layer; forming an N-type transistor in and above said N-active region; and forming a P-type transistor in and above said P-active region.
 2. The method of claim 1, wherein said first semiconductor material is comprised of silicon.
 3. The method of claim 1, wherein said second semiconductor material is comprised of silicon-germanium or a III-V material.
 4. The method of claim 2, wherein said second semiconductor material is comprised of silicon-germanium or a III-V material.
 5. The method of claim 1, wherein prior to forming said first masking layer, the method further comprises performing a common etching process to form recesses in said N-active region and said P-active region.
 6. The method of claim 1, wherein said N-type transistor and said P-type transistor are planar transistors or FinFET transistors.
 7. The method of claim 1, wherein said N-active region is defined by a first isolation region positioned in said substrate and said P-active region is defined by a second isolation region positioned in said substrate, and wherein the method further comprises: performing said common deposition process such that an upper surface of said first portion of said layer of a first semiconductor material is substantially level with an upper surface of said first isolation region; and forming said layer of said second semiconductor material is performed such that an upper surface of said layer of said second semiconductor material is substantially level with an upper surface of said second isolation region.
 8. A method, comprising: forming an N-active region and a P-active region in a semiconductor substrate; performing a common etching process to form recesses in said N-active region and said P-active region such that said N-active region and said P-active region have recessed surfaces; forming a first masking layer that covers said P-active region while leaving an area above said N-active region un-masked; with said first masking layer in position, forming a layer of silicon-carbon on said recessed surface of said N-active region; removing said first masking layer; performing a common deposition process to form a first portion of a layer of silicon on said layer of silicon-carbon and a second portion of said layer of silicon on said recessed surface of said P-active region; forming a second masking layer that covers said N-active region while leaving an area above said P-active region un-masked; with said second masking layer in position, forming a layer of a first semiconductor material on said second portion of said layer of silicon; removing said second masking layer; forming an N-type transistor in and above said N-active region; and forming a P-type transistor in and above said P-active region.
 9. The method of claim 8, wherein said second semiconductor material is comprised of silicon-germanium or a III-V material.
 10. The method of claim 8, wherein said N-active region is defined by a first isolation region positioned in said substrate and said P-active region is defined by a second isolation region positioned in said substrate, and wherein the method further comprises: performing said common deposition process such that an upper surface of said first portion of said layer of silicon is substantially level with an upper surface of said first isolation region; and forming said layer of said first semiconductor material is performed such that an upper surface of said layer of said first semiconductor material is substantially level with an upper surface of said second isolation region. 